Many multi-room structures, such as office buildings and schools as well as residential buildings constructed during the past several years, include heating and cooling systems to deliver either relatively warm or cool conditioned air from a central source thereof to each of the enclosures or rooms in the building. Typically, one or more ducts are employed to deliver the air to each enclosure. Very often, an automatically operated damper blade assembly or similar mechanism is installed in the duct to regulate the flow of air to one or more discharge outlets located in the enclosure being conditioned by the discharge of air thereinto. The movement of the damper blade assembly may be responsive to changes in the temperature of the enclosure.
Many of these automatically operated damper blade assemblies use a spring to open the damper and an opposing electric motor and gear train assembly to close the damper and hold it in the closed position when conditioned air is not needed in the enclosure. The damper, the spring, the motor and its gear train assembly are interconnected such that as the motor closes the damper it also acts against the spring. When the motor is de-energized, the spring reacts to open the damper and in doing so rotates the motor shaft in the direction opposite its drive direction until the damper reaches an end stop defining its open position.
Certain problems, however, arise when the exact requirements of the damper blade assembly are examined. On the one hand, a relatively strong opening force for the spring is required to ensure that any friction or binding forces on the moving parts of the damper blade assembly will be overcome. On the other hand, the gear train associated with the motor is relatively fragile and will not withstand much in the way of an impact such as can be caused when a moving gear train is stopped suddenly. As a strong spring force drives the damper to an open position, it is subjecting the gear train to a substantial amount of torque. In currently used damper blade assemblies, when the damper reaches the end of its travel towards the open position and contacts an end stop, this torque is transferred to the gear train as an impact force with the result that the gear train may be damaged. Similarly, the gear train can easily be damaged if the damper blade assembly is turned by hand with too much force. This sometimes occurs during the packaging and installation of the system. While some vendors include a shock absorbing spring and add play to the assembly to reduce the chance of over-stress damage, wear of the gears continues to limit the life of the damper blade assembly. The cost of the damper blade assembly is high due to the number of parts and tolerances required.
Accordingly, it remains a challenge to construct a mechanism that can maintain the narrow balance between too powerful a spring which will damage the gear train and too weak a spring which will not be able to overcome the friction and drag that will generally increase as the damper becomes worn during its service life. In addition, it remains desirable to prevent over-stress damage to the damper blade assembly by permitting the gear train and the motor to slowly decelerate instead of causing the impact that occurs in the conventional mechanisms when they suddenly stop and the damper hits its end stop in the open position.